Action: Reintroduce primates in groups

Key messages

Two studies in Braziland Thailand found that populations of introduced primates declined after reintroduction in groups, alongside other interventions, while one study in Belize recorded an increase in populations. Two studies in Madagascar and India found that primate populations persisted 4-55 years after reintroduction in groups, alongside other interventions.

Seven studies in Brazil, French Guiana, Madagascar, and South Africa found that a minority of primates survived for at least 15 weeks to seven years after reintroduction in groups, alongside other interventions. Seven studies in Belize, Brazil, French Guiana, Madagascar, and South Africa found that a majority of primates survived after between two and thirty months.

One study in Madagascar found that introduced black-and-white ruffed lemurs Varecia variegata had similar diets to individuals in a wild population after reintroduction in groups, alongside other interventions.

One study in The Gambia found that a population of introduced chimpanzees increased 25 years after reintroduction in groups, alongside other interventions. Four studies in Guinea, Liberia and the Republic of Congo found that the majority of chimpanzees survived for at least two to five years, after reintroduction in groups, alongside other interventions.

Two before-and-after studies in Gabon and the Republic of Congo found that the majority of western gorillas survived for at least nine months to four years, after reintroduction in groups, alongside other interventions.

One controlled study in Indonesia found that all Sumatran orangutans survived for at least three months after reintroduction in groups, alongside other interventions.

Supporting evidence from individual studies

1

A study in 1967-1985 in a coastal rainforest on Nosy Mangabe island in Madagascar found that populations of aye-ayes Daubentonia madagascariensis, white-fronted lemurs Eulemur albifrons and black-and-white ruffed lemurs Varecia variegata variegata that were reintroduced as groups, had persisted at least 18 years (aye-ayes) and 55 years (white-fronted lemurs, black-and-white ruffed lemurs) post-release. One aye-aye was sighted in 1975, two in 1981, a mother and her infant in 1983 and another two individuals in 1984. At least four groups of white-fronted lemurs and eight groups of black-and-white ruffed lemurs appeared live on the island in 1984. A group of nine (four females and five males) aye-ayes caught in different locations were released on the island in 1967. It is unclear whether wild aye-ayes occurred on the island before reintroduction. An unknown number of white-fronted lemurs and black-and-white ruffed lemurs were released on the island in the 1930s. No systematic surveys were conducted on the island.

2

A before-and-after trial in 1954-1985 in degraded rainforest in Poço das Antas Reserve, Brazil found that translocated captive-born golden lion tamarin Leontopithecus rosalia, some of which were released in groups along with nine other interventions, decreased in numbers by more than half (57%) within the first year post-release. No statistical tests were carried out to determine whether this decrease was significant. Of the 14 individuals released, seven died (50%) and two were removed. Three infants were born, one of which died. Eight individuals were released as a family group and six individuals were released as pairs one month later. Tamarins spent an unknown amount of time in 15 x 4.5 x 3 m outside enclosures to acclimatize. They were habituated to humans and fostered to facilitate survival in the wild. The reserve included natural predators. Sick or injured tamarins were captured and treated. Reintroduced tamarins were supplied with food for ten months post-release. Artificial nesting boxes, which were hollow logs provided to them during training, were provided. The study does not distinguish between the effects of the different interventions mentioned above.

3

A before-and-after trial in 1984-1991 in coastal forest in Poço das Antas Reserve, Brazil found that the majority of golden lion tamarins Leontopithecus rosalia that were reintroduced as groups into natural habitat along with 14 other interventions, did not survive over seven years. Fifty-eight out of 91 (64%) reintroduced tamarins did not survive post-release. However, 57 infants were born (reproductive rate=63%) during this period, of which 38 (67%) survived. Different groups of captive-bred or orphaned tamarin groups were introduced in 1984-85, 1987, and 1988-90 into habitat already occupied by the species and predators. Some groups were trained to learn behaviours that facilitated survival, were provided with supplementary food, water and nesting boxes, and were allowed to adapt to local habitat conditions before release. Tamarins were quarantined, underwent veterinary checks and parasite treatments before release. Reintroduced sick or injured animals were rescued, treated and re-released. The reserve became protected in 1983. The study does not distinguish between the effects of the different interventions mentioned above.

4

A study, which was included in a review, in 1976-1977 in dry evergreen forest in Sai Yok National Park, Thailand found that captive lar gibbons Hylobates lar that were partially released in family groups alongside- other interventions decreased in numbers by 6% and no infants were born during 17 months post-release. No statistical tests were carried out to determine whether this decrease was significant. Four gibbons joined wild groups. A total of 31 gibbons were introduced as individuals, pairs, or family groups into habitat with resident wild gibbons. Anaesthetized gibbons were either kept in separate cages from which they could hear but not see each other for 14 days before release, or laid out on the forest floor. Injured animals were recaptured and treated. In 1961, gibbons became protected in Thailand. Reserve staff was permanently present. The study does not distinguish between the effects of the different interventions mentioned above.

5

A replicated study in 1992–1993 in tropical forest at Cockscomb Basin Wildlife Sanctuary (CBWS) in Belize found that the majority of reintroduced black howler monkeys Alouatta pigra that were released in three groups alongside other interventions, survived for at least ten months and reproduced. Twelve out of 14 reintroduced monkeys (86%) survived for at least ten months post-release. One male and juvenile disappeared after two months. One group of four monkeys dissolved following aggressive interaction with another release group. One female dispersed with her infant and one female stayed alone. Two infants were born, in two release groups, 3-8 months post-release. Three groups, consisting of 3-7 individuals, were released 0.5-1 km apart into habitat without resident howlers. Wild howlers were captured at the Community Baboon Sanctuary and translocated to CBWS. Prior to release, howlers underwent veterinary screens. They were allowed to adapt to local conditions before release. Six individuals were fitted with ball-chain radio-collars and another six individuals were implanted with radio-transmitters. Radio-transmitter signals got lost six weeks after release. The study does not distinguish between the effects of the different interventions mentioned above.

6

A before-and-after trial in 1994 in tropical forest at Fazenda União, Rio das Ostras, Brazil found that the majority of golden lion tamarins Leontopithecus rosalia that were translocated from small, isolated and degraded forest patches outside of the study area and reintroduced in groups into their new habitat where the species was already present, survived for at least two months. All seven monkeys (five adults and two infants) that were captured and translocated survived for at least two months after their release and extended their range over time. No statistical tests were carried out to determine whether this increase was significant. Two other individuals from another forest patch were captured, fitted with radio-collars and followed for 15 days. One tamarin was killed by a domestic dog Canis familiaris domesticus and the other one illegally captured before they could be translocated. Tamarin groups were captured by baited traps, weighed, tattooed and all adults were fitted with radio-collars before release.

7

A before-and-after trial in 1992-1994 in tropical forest in Cockscomb Basin Wildlife Sanctuary in Belize found that the population of wild black howler monkeys Alouatta pigra that was reintroduced in groups alongside other interventions, increased by more than 60% in five years. By 1997, the population had increased from 62 to 100 individuals. However, no statistical tests were carried out to determine whether this increase was significant. One-month to 2-year survival rates for the different cohorts released in the dry seasons of 1992-1994, were 81-100%. Birth rate was 20% (N=12) and infant survival rate was 75% (N=9). Entire social groups were reintroduced together, and ten of the 14 groups were held in cages for 1-3 days before release into habitat without predators and with a distance of 700-1000 m to the neighbouring troop. All individuals underwent veterinary screens, were individually marked, and adults were fitted with radio-collars. Hunting was largely controlled in the sanctuary and the local community was educated about the reintroduction project and the importance of black howler conservation through multimedia campaigns. The study does not distinguish between the effects of the different interventions mentioned above.

8

A study in 1987-1988 on an island in tropical forest in Liberia found that the majority of western chimpanzees Pan troglodytes verus, that were reintroduced in groups alongside other interventions, survived for at least one year on a natural island. Seven out of 30 released chimpanzees had difficulties to adjust to the new social environment and were brought back to captivity. Chimpanzees were reintroduced in subgroups. Before release, chimpanzees were screened for diseases, were socialized in naturalistic enclosures and were taught behaviour to facilitate their survival in the wild. On site, chimpanzees were allowed to adapt to the local habitat in enclosures for some time; younger and low-ranking individuals were released earlier to reduce stress. Released chimpanzees were continuously provided with food. Sick and injured animals were temporarily removed and treated. The study does not distinguish between the effects of the different interventions mentioned above.

9

A study in 1994-1995 in primary forest at Petit Saut hydroelectric dam in French Guiana found that less than half of the monitored red howler monkeys Alouatta seniculus that were translocated and reintroduced into their new habitat in groups along with other interventions, survived over 18 months. Of the 16 females monitored for 18 months, seven (44%) females survived with a possible survival rate of 63%. Deaths included screwworm fly larvae infestations under radio-collars (N=2) and trauma (N=1). Three (19%) females gave birth after release, but all infants disappeared and probably died. All females studied for longer than three months (50%) settled within the release area. Of the 28 different translocated troops (122 individuals) ten out of 11 (91%) documented troops broke apart post-release. All animals underwent veterinary screens before t release into habitat already occupied by the species. They were allowed to adapt to local habitat conditions for some time before their release. The study does not distinguish between the effects of the different interventions mentioned above.

10

A study in 1999 in tropical forest of Morro do Diabo State Park, Brazil found that only some of the reintroduced wild and captive-bred black lion tamarins Leontopithecus chrysopygus that were released in one group along with other interventions, survived over four months. Four months after the release of three individuals, one tamarin died. The group consisted of two wild females and one captive-born male which was bred in a free-ranging environment to facilitate reintroduction. The male was treated after becoming sick. Tamarins underwent veterinary screens before translocation to an enclosure at the release site where they could adapt to the local environment with predators. Tamarins were fitted with radio-transmitters and supplemented with food. The study does not distinguish between the effects of the different interventions mentioned above.

11

A before-and-after trial in 1996-1999 in tropical rainforest in Conkouati Reserve, Republic of Congo found that 70% of reintroduced wild-born orphaned chimpanzees Pan troglodytes troglodytes that were released in groups along with eight other interventions, were still alive 3.5 years after release. Estimated mortality was 10-30%. None of the adult females reproduced. Chimpanzees fed on 137 different plant species, a variety similar to that of wild chimpanzees. They also had activity budgets that resembled those of wild chimpanzees. No statistical tests were carried out to determine whether these similarities were statistically valid. Before reintroduction into habitat with low densities of wild chimpanzees, they spent 6-9 years on one of three forested islands in the region to acclimatize. Release groups were small and composed of individuals that had formed strong associations during acclimatization. Chimpanzees underwent veterinary screens, were treated for endoparasites and vaccinated for poliomyelitis and tetanus. Orphan chimpanzees were rehabilitated and fostered. Researchers were permanently present on-site and monitored released chimpanzees using radio-collars. The study does not distinguish between the effects of the different interventions mentioned above.

12

A before-and-after trial in 1994-1999 in tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of central chimpanzees Pan troglodytes troglodytes that were reintroduced in groups along with 16 other interventions, survived over five years. Out of 20 reintroduced chimpanzees released in four subgroups from 1996-1999, 14 survived (70%). No statistical tests were carried out to determine whether the population decrease was significant. Individuals were radio-collared. Rehabilitated orphaned chimpanzees underwent vaccination, treatment for parasites and veterinary screens before translocation from the sanctuary to the release site where resident chimpanzees occurred. Staff members were permanently present to monitor primate health, provide additional food if necessary and examine dead animals. The area status was upgraded from reserve to national park in 1999. Local people were relocated from the release site to a nearby village. Some chimpanzees were treated when sick or injured. TV and radio advertisements were used to raise chimpanzee conservation awareness and local people were provided monetary and non-monetary benefits for their conservation support. The study does not distinguish between the effects of the different interventions mentioned above.

13

A before-and-after trial in 1994-1995 in tropical forest near Petit-Saut dam, French Guiana found that most translocated white-faced sakis Pithecia pithecia that were partly released as a group along with other interventions, survived over four months. Two of six translocated sakis survived over four months after release. Three individuals released as a group dispersed separately after release and one male of this group associated temporarily with a resident couple before becoming solitary. Only three translocated wild sakis were monitored over 41 weeks post-release, which took place one day after capture. Monkeys were captured by nets, radio-collared and underwent veterinary screens prior to release. Dead sakis were examined to establish their cause of death. One male died from a parasite infection. The study does not distinguish between the effects of the different interventions mentioned above.

14

A replicated, before-and-after-trial in 1995-2001 in temple orchards in urban Vrindaban, Mathura District, India found that rhesus monkeys Macaca mulatta reintroduced in groups into forest patches along with other interventions remained at their release sites over four years. A post-translocation study in 2001 confirmed that all of the 600 monkeys captured from 12 troops (45% of total population) and translocated to eight different forest patches, had settled down, were healthy and behaved normally. Time spent engaging in different activities for one of the translocated groups (150 individuals) during the first three months post-release was similar to wild groups in northern India. No quantitative results were provided in this study. Attempts were made to capture as many animals as possible from a single social group whenever a troop of monkeys was encountered. Captured monkeys, which were regarded as so-called ‘problem’-animals by local residents, were translocated to non-residential, natural habitat without resident monkeys. The study does not distinguish between the effects of the different interventions mentioned above.

15

A before-and-after trial in 1998-1999 in tropical forest on an island in French Guiana found that a small number of reintroduced squirrel monkeys Saimiri sciureus that were released as a group along with other interventions, survived over 15 weeks post-reintroduction. Six (43%) out of 14 released monkeys survived over 15 weeks, after which monitoring ceased. Two individuals died in their release cages, and one was apparently killed by resident wild monkeys. One month after release, five monkeys were recaptured and brought back to captivity. The remaining six monkeys were wild-born; dead and removed individuals were captive-born monkeys. Animals were kept as one group in an isolated cage at the captive colony where two females gave birth. After transfer to the release site, monkeys were held in an enclosure to adapt to local habitat conditions. The study does not distinguish between the effects of the different interventions mentioned above.

16

A controlled study in 1998-2001 in tropical forest in Betampona Reserve, Madagascar found that diets of captive-bred, reintroduced black-and-white ruffed lemurs Varecia variegata variegata that were born and reared in cages and introduced in groups along with other interventions, did not overlap with that of the resident wild group in the first year post-release. No statistical tests were carried out to determine whether this overlap was significant. Captive-bred lemurs (one male and two females) fed only on slightly more than half of the plant species (N=57 plants) that the wild group (N=10 individuals) fed on (N=109 plants). Captive-bred lemurs did not closely follow the dietary choices and seasonal changes in diet exhibited by the wild group. Lemurs were provided with supplementary food during the entire study period. They were reintroduced into habitat already occupied by the species. The study does not distinguish between the effects of the different interventions mentioned above.

17

A controlled study in 2001 in tropical forest in Betampona Reserve, Madagascar found that diets of captive-bred, reintroduced black-and-white ruffed lemurs Varecia variegata variegata that had limited free-ranging experience before release and that were reintroduced in groups along with other interventions, overlapped with that of the resident wild group. Reintroduced lemurs (three males and one female) fed on 54 species during a single year, as compared to the wild group (N=10 individuals) that fed on 109 species over four years. Furthermore, reintroduced lemurs consistently consumed less foliage than the wild group did throughout the study, although no statistical tests were carried out to determine whether this difference was significant. Lemurs were provided with supplementary food during resource-scarce periods only and were reintroduced into habitat already occupied by the species. The study does not distinguish between the effects of the different interventions mentioned above.

18

A controlled study in 1997-2001 in tropical forest in Betampona Reserve, Madagascar found that diets of captive-bred, black-and-white ruffed lemurs Varecia variegata variegata that were born and raised in a free-ranging environment and reintroduced in groups along with other interventions, overlapped with that of the resident wild group. No statistical tests were carried out to determine whether this overlap was significant. Reintroduced lemurs (three males and two females) fed on 92 species over three years, as compared to the wild group (N= 10 individuals) that fed on 109 species over four years. Reintroduced lemurs consumed less foliage throughout the study and less nectar in 1998 than the wild group did. No statistical tests were carried out to determine whether this difference was significant. Two reintroduced males died of malnutrition in 1998 due to climate change and seasonal food shortages. Lemurs were reintroduced into habitat already occupied by the species and were provided supplementary food during resource-scarce periods. The study does not distinguish between the effects of the different interventions mentioned above.

19

A before-and-after trial in 1997-2002 in primary forest in Betampona Reserve, Madagascar found that less than half of all captive-bred, parent-reared black-and-white ruffed lemurs Varecia variegata variegata that were reintroduced in groups along with ten other interventions, survived until the end of the study period of five years. Five (38.5%) of 13 individuals survived in the wild and six individuals were born, of which four survived. One female and one male reproduced with resident wild lemurs and the male became fully integrated. Lemurs were released as either family groups or constructed pairings. All released animals were fitted with radio- collars. Captive lemurs had limited semi-free-ranging experience, were quarantined and underwent veterinary screens before their reintroduction into habitat with predators and resident wild lemurs. They were recaptured and treated when sick and provided with supplementary food and water for a certain period of time. They were allowed to adapt to local habitat conditions before release. Dead lemurs were examined. The study does not distinguish between the effects of the different interventions mentioned above.

20

A study in 1979-2004 in tropical forest on Baboon Islands, River Gambia National Park, The Gambia found that rehabilitated western chimpanzees Pan troglodytes verus that were reintroduced in groups along with other interventions, increased from 50 to 69 chimpanzees over 25 years. No statistical tests were carried out to determine whether this increase was significant. Fertility and mortality rates were similar to wild chimpanzees, except for infant mortality (18%), which was lower than in wild populations. Inter-birth interval, average age at first birth, proportion males at birth, age at first sexual swelling in females, and adolescent infertility were similar to wild chimpanzees. In total, 50 chimpanzees from various backgrounds were released on three islands. Individuals were reintroduced into habitat with no wild or previously reintroduced chimpanzees and with small populations of natural predators. They were continuously provided supplementary food every 1-2 days. Individuals received periodic deworming and antibiotic treatment when they suffered severe colds. The study does not distinguish between the effects of the different interventions mentioned above.

21

A study in 2002–2006 in rainforest in Lékédi Park, Gabon found that one third of captive-bred mandrills Mandrillus sphinx that were reintroduced in groups alongside other interventions, died within the first year post-release. Mortality was 33% (12 individuals of 36), mostly affecting infants. Fertility rate was 42% (5 of 12 females reproduced), and two of the five infants survived for longer over six months. Mortality decreased to 4% in the second year and fertility rate remained at 42%, but all five infants survived over six months. Their range remained limited during the first two years post-release. In 2006, the group numbered 22 individuals, including 12 of the mandrills originally released, all in good physical condition. Mandrills were transferred to the release site in two groups and released all together in 2002. Mandrills were reintroduced into habitat already occupied by the species and with predators; they were allowed to adapt to local habitat conditions for some time, and were treated for endoparasites before release. Mandrills were also supplemented with food until 2005. The study does not distinguish between the effects of the different interventions mentioned above.

22

A before-and-after trial in 2006-2007 in rainforest in Analamazaotra Special Reserve, Madagascar found that black-and-white ruffed lemurs (BWRL) Varecia variegata variegata and diademed sifakas Propithecus diadema that were reintroduced in their social groups after translocation from disturbed sites to undisturbed habitat along with other interventions, survived over 30 months and reproduced. No mortalities were recorded for BWRL over a 30-month observation period and only one diademed sifaka died from natural causes. Two sets of BWRL twins (reproductive rate=57%) and seven diademed sifaka infants were born (reproductive rate=26%), the latter of which only two survived. A total of seven BWRL and 27 diademed sifakas were captured at four disturbed forest sites and released in the reserve where the species had locally gone extinct and that included natural predators. Released primates were habituated to human presence and monitored using radio-collars. Two to eight months before a translocation was carried out, lemurs were darted and underwent veterinary checks. The study does not distinguish between the effects of the different interventions mentioned above.

23

A controlled study in 2004-2005 in secondary tropical forest in Bukit Tigapuluh National Park, Central Sumatra, Indonesia found that all reintroduced Sumatran orangutans Pongo abelii that were released in groups along with other interventions, survived for at least three months. Eight captive orphaned orangutans with largely unknown histories were released in two groups and all survived for at least three months post-release. One group was directly released into the forest after a 6-month acclimatization phase at a sanctuary. Another group of individuals was kept in semi-free conditions for 7-9 months prior to release and allowed to overnight in the enclosure. Staff members guided the latter group daily to the forest. Orangutans underwent quarantine and were medically screened before being released to re-establish populations in habitat where previously released orangutans occurred. Supplementary food was provided regularly. The study does not distinguish between the effects of the different interventions mentioned above.

24

A before-and-after trial in 2007-2008 in dry forest-grassland mosaic near Richmond, South Africa found that a small number of vervet monkeys Chlorocebus aethiops that were released in two groups along with other interventions, survived over ten months post-reintroduction. Out of 35 monkeys released in troop one, only six (17%) survived for ten months post-release, when monitoring ceased. Twenty-two (63%) vervets went missing and seven (20%) died. However, two infants were born 10-11 months post-release. Out of 24 vervets released as troop two, 12 (50%) survived, seven (29%) went missing and five (21%) died. Groups were released five days apart. Monkeys underwent veterinary checks, and were allowed to adapt to local environmental conditions before their release into habitat already occupied by the species. They received supplementary food and water after their release. The study does not distinguish between the effects of the different interventions mentioned above.

25

A study in 2007-2010 in subtropical forest-shrubland mosaic in Mondi forestry, South Africa found that one third of the 31 rehabilitated vervet monkeys Chlorocebus aethiops that were reintroduced as a group alongside other interventions, survived over 12 months. One year post-release, ten (32%) individuals had survived and 20 (65%) vervets could not be tracked. One individual was euthanized three days post-release after raiding houses and acting aggressively towards people. One week post-release, the group split into two groups. The release group included both wild captured- (61%) (due to injury) and hand-raised orphaned (39%) monkeys. Monkeys underwent veterinary screens, were held in an enclosure to adapt to local habitat, and were supplemented with food for eight weeks. Eleven individuals were fitted with radio-collars. The study does not distinguish between the effects of the different interventions mentioned above.

26

A before-and-after trial in 2008-2010 in dry forest-savanna mosaic in Mafou forest, Haut Niger National Park, Guinea found that the majority of wild-born orphaned western chimpanzees Pan troglodytes verus that were reintroduced in a group along with other interventions, survived reintroduction and remained free-living for at least 27 months. One out of 12 (8.3%) released chimpanzees died from anaesthesia during a recovery mission. One female returned to the sanctuary voluntarily and one male was returned after suffering injuries. Five chimpanzees (42%) remained together at the release site and two females gave birth and both infants survived. Another female dispersed to a wild chimpanzee community and three chimpanzees moved to an area away from the release site. Chimpanzees were released simultaneously from release cages (5 adult males) or individual transport cages ca. 100 m away (6 females, 1 young male). All chimpanzees were screened for diseases before their release into habitat with wild chimpanzees and predators. Chimpanzees were initially daily supplemented with food, and later on, a weekly . The study does not distinguish between the effects of the different interventions mentioned above.

27

A before-and-after trial in 2009-2010 in coastal forest in Ntendeka Wilderness Area, Ngume Forest, South Africa found that 56% of captive, wild-born vervet monkeys Chlorocebus aethiops that were reintroduced as a group along with other interventions, survived for at least six months post-release. Three (19%) individuals were reported dead, two killed by predators and one by domestic hunting dogs Canis lupus familiaris. Four individuals (25%) went missing. One female gave birth two weeks post-release. Monkeys were introduced as one troop of 16 individuals (11 males, 5 females) where sex and age composition of the troop was similar to wild troops. The troop was released into habitat without resident vervets, but with predators. To acclimatize, monkeys spent one day in a release enclosure (49 m2). They were provided supplementary food twice per day for two weeks and once per day for a further three weeks post-release. The release site became a nationally protected wilderness area. The study does not distinguish between the effects of the different interventions mentioned above.

28

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of western lowland gorillas Gorilla gorilla gorilla, reintroduced in groups along with 14 other interventions, survived for at least four years. Twenty-one (84%) of 25 gorillas released in Congo and 22 (85%) of 26 gorillas released in Gabon survived over four years. Nine females gave birth to 11 infants, of which nine survived. In Gabon, two groups were reintroduced in 2001 and 2004 and in Congo, five groups were reintroduced in 1996-2006. Gorillas underwent disease screening during quarantine and received preventative vaccinations. Gorillas were allowed to adapt to local environment and were supplemented with food prior to release. Gorillas were released into habitat with no resident gorillas. Released gorillas were treated for parasites and when sick. So-called ‘problem’-animals were removed and relocated and bodies of dead gorillas were examined. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-borns. Both sites became protected areas before reintroduction commenced. The study does not distinguish between the effects of the different interventions mentioned above.

29

A before-and-after trial in 2008 in a coastal forest at Isishlengeni Game Farm, South Africa found that over 60% of rehabilitated vervet monkeys Chlorocebus aethiops that were reintroduced as one large troop into the wild along with other interventions, survived for at least six months. Five (17%) of 29 introduced individuals were reported dead. Of these, one was predated and four were killed by domestic hunting dogs Canis lupus familiaris. Six (21%) individuals went missing. No females reproduced. The release troop included 29 individuals (18 males, 10 females, 1 infant), where sex and age composition of the troop differed significantly from that of wild troops. Monkeys were released into habitat already occupied by wild vervets and with predators. To acclimatize, monkeys spent two nights in a release enclosure (49 m2) before being released. Monkeys were provided daily supplementary food. Medical care was provided when necessary before release and while housed at the nearby rehabilitation centre. The study does not distinguish between the effects of the different interventions mentioned above.

30

A before-and-after trial in 2008-2010 in a tropical forest-grassland mosaic at Batéké Plateau National Park, Gabon found that the majority of western lowland gorillas Gorilla gorilla gorilla that were reintroduced as a group alongside ten other interventions, survived for at least nine months. Four out of five (80%) juvenile gorillas survived over nine months post-release. After the death of the youngest individual, group cohesion decreased. Three captive-bred and two orphaned wild born individuals were reintroduced into habitat with predators and without resident wild gorillas after they were allowed to adapt to local habitat conditions for some time. They spent the night in an enclosure equipped with nesting platforms, nesting material, supplementary food and water. Gorillas were dewormed regularly on-site. Caretakers guided them daily into different forest patches. The study does not distinguish between the effects of the different interventions mentioned above.

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